1. Field of the Invention
The present invention relates to a control of an amount of flash light when imaging using a light emitting device is performed.
2. Description of the Related Art
In taking an image of an object by flash imaging using a light emitting device, there is a method that determines an amount of flash light by executing preliminary flash. According to this method, the preliminary flash is executed by using the light emitting device before the main imaging and the amount of light reflected from the object is obtained. Then, the amount of flash light of the main imaging is calculated based on the reflected light acquired at the preliminary flash. For example, Japanese Patent Application Laid-Open No. 2005-275265 discusses a method for determining an amount of flash light according to the calculation described below.
First, a ratio R(i) of a luminance value H(i) at the preliminary flash for each of the light metering areas A0 to A22 to an object luminance value P(i) just before the preliminary flash for each of light metering areas A0 to A22 are calculated.
Next, the greatest value of the ratios R(i) of the light metering areas A0 to A22 is extracted as a reference value baseR. The light metering areas, which are used as target areas when the light metering area whose ratio R(i) is the reference value baseR is extracted, are the light metering areas whose reflected amount of light is between threshold values LVL0 and LVL1 which are set according to a distance to the object at the preliminary flash.
Further, in determining the light metering areas which are used as target areas when the light metering area whose ratio R(i) is the reference value baseR is extracted, if a mounted lens unit has a distance encoder, the threshold values LVL0 and LVL1 are set based on the information obtained from the distance encoder. If a mounted lens unit does not have a distance encoder, the threshold values LVL0 and LVL1 are set according to a distance determined according to past experience.
The extracted reference value baseR and the ratio R(i) of each of the light metering areas A0 to A22 are compared and a weighting coefficient W(i) of each of the light metering areas A0 to A22 is obtained. By using the obtained weighting coefficient W(i), a weighting calculation of the reflected light of the object is performed. Further, by using the result of the weighting calculation, the amount of flash light when imaging is performed is calculated.
According to the method discussed in Japanese Patent Application Laid-Open No. 2005-275265, stable exposure is obtained in many scenes. Further, imaging results of small exposure variance can be obtained when imaging of a same scene but with a slightly different composition is performed.
However, since the weighting coefficient W(i) is increased based on a main object area, which is a light metering area that satisfies predetermined conditions and whose R(i) is the largest, if the object is located at a comparatively short distance or if an item with a high reflectivity is included in the imaging screen, the weighting coefficient W(i) may be increased.
For example, if a highly-reflective object, such as a gilded folding screen, is included in the imaging screen, and further, if the accuracy of the distance encoder information obtained from the distance encoder mounted on the lens unit is not high or the distance is determined according to past experience because the lens unit does not have a distance encoder, the light metering area including the gilded folding screen is regarded as the main object area. In such a case, since the weighting coefficient W(i) of the light metering area including the gilded folding screen is increased when the amount of flashlight is calculated, the amount of flash light may not be sufficient for the imaging of the main object, resulting in underexposure.